Like any technical device, electrical machines may suffer from different kind of faults, either of mechanical or electrical character. Since electrical machines have a moving element in form of a rotor, many of the most common fault conditions cause vibrations to the machine. It is known that different fault conditions cause different kind of vibrations. In turn, it follows that by knowing what kind of vibration a certain fault condition causes, it is possible to detect the fault by monitoring the vibration characteristics of the machine.
Vibration monitoring has been conventionally used to detect mechanical faults in electrical machines. This monitoring method has been successful e.g. in detecting bearing defects. However, one has not been able to detect electrical faults in a satisfactory way by means of vibration monitoring, even if attempts into this direction have been taken. For example, the conference paper “An analytical approach to solving motor vibration problems” from Finley, W. R. et al. 1999 (D1) discloses a table (Table I) with indicators for identifying both mechanical and electrical faults in an induction motor. The main fault indicators are the frequencies of the vibrations and their sidebands. It requires a lot of empirical interpretation to determine the root source of the vibration with the help of D1, and it is not possible to distinguish between different fault conditions in a satisfactory manner.